Amplifier system, method, and apparatus



March 29, 1932. 1,851,587

E. H. LOFTlN ET AL AMPLIFIER SYSTEM, METHOD, AND APPARATUS Filed July 22, 1927 5:5 l/fz j @f 70 Alla/O +B HIGH INVENTORS- fan/,4R0 /v off/N Patented Mar. 29, 1932 UNITED STATES PATENT ori-ICE f7 EDWARD H. 'LOFTIN AND ASIDNEY Y. WHITE, OF NEW YORK, N. Y., ASSIGNORS, BY MESNE ASSIGNMENTS, TO RADIO CORPORATION 0F AMERICA, 0F NEW YORK, N. Y., A COR- ]?ORATION 0F DELAWARE AMPLIFIER SYSTEM, METHOD,

AND APPARATUS Application mea July 22, 1927. Vser-iai 110.2073618.

While our invention relates generally to amplifier systems, it refers particularly to such systems including three electrode vacuum tube or like operating amplifiers, and has for a particular object the efcient amplification of alternating currents of moreor less high frequency. f

` Another object is to choose and selectively amplify such currents over a Wide band of frequencies While maintainingthe amplification efliciency practically uniform with frequency, or to be able to vary the efficiency in any desired manner With frequency.

A further object is to provide an amplifying system that is oscillation proofed, and is free from troublesome reaction of the-circuitsk of the system upon each other.

Still further obiects are the simplification of selective control of amplification andthe elimination of some of the difficulties that have heretofore been encountered in multiple stage amplification, particularly of the high frequency character. a

Our invention Will be best understood by reference to the figures of the accompanying drawings in Which Fig. 1 is an explanatory diagram, and Figs. 2 and 3 are ldiagrammatic representations of tWo different embodiments of our invention shown employed for illustrative purposes in radio receivers. Like reference symbols in the several figures represent like parts.

In Fig. 1 the three electrode vacuum tube VT1 is shown to have an input circuit including a tunable circuit 1 with whichv is associated a. source of alternating currents S, it being assumed for explanatory purposes that the frequency of the alternating currents Y q can be varied over a range, and circuit 1 can be tuned in consonance with such variations.

The output circuit is shown coupled to a P second tube VT2 with the aid of an indicated non-selective impedance I, which impedance may be a more or less high resistance, a condenser, or a so-called choke or capacitively reacting coil. l The capacity C1 represented in dotted lines indicates the so-called internal or plate-to-grid capacity of tube VTi, and the capacity CD in dotted lines represents the distributed capacity of the leads and other elements of the output circuits. For simplicity means for energizing the tubes for operation have been omitted in this explanatory figure, it being understood that the operation tobe explained refers to a properly energized system. e i Considerable effort has been made in practice to couple amplifiers through fixed impedances in the manner shown in Fig. l with the hope that energy would be substantially equally Well transferred for all frequencies,

or in other Words to'make the lsystemva so-Y called universal amplifier,b`utsuch poor results have been secured in Vhigh frequency Work in the matter of securing efficient amplification that such systems havel practically found no use in the art. The poor lamplifying results come about by reason of thefact that no matter' What may be the form of the fixed impedance there results an over-'all plate circuit reactance that is capacitive in nature, so that the reaction of the plate circuit onto the grid circuit throughfthe so-called gridto-plate capacity of the tube, or inter-electrodalcapacity indicated as C1, has the well known'eect of being of incorrect phase to assist the incoming energy in the grid circuit, but rather opposes it, so that lthe tube is caused to de-amplify from its normal amplifying ability. In fact, such an arrangement used in the kilocycle band'ofOO to 1500 of radio broadcasting is practically Worthless as an amplifier. Inaddition, the reactance is not constant lwith frequency. so that the tube isV caused to de-amplify to different degrees for different frequencies.,A With the result that the poor results are not uniform Withvfreuency." y 7 If the impedance I is inthe form of a rather high resistance the overall reactance of the late circuit is necessarily capacitive,because of the distributed capacity indicated at GD.

If the impedance isa condenser the overall reactance is necessarlly capacitive. If i the impedance is a so-calledchoke coil, to be effective as an impedance it must necessarily react capacitively, cuit reactanceis capacitive.

Our invention overcomes these difficult is,

the first embodiment of it being shown 'n so that the overall plate cir- Fig. 2, in which the element A is an ordinary Y radio receiving antenna connected to ground at G, theantenna being coupled to a variable period circuit L2C2 through a combined electromagnetic and electrostatic coupling including lthe inductive relation between coils L1 and L2 and coupling condenser C1. The manner in which 'such a combined coupling can be made to transfer substantially constant energy with frequency, or vary the transfer inany predetermined manner with ment is somewhat removed from Y tube amplifier VTl. This first tube frequency, is fully disclosedin zthe copendingapplication of S. Y. White, Serial N o. 48,936, filed August 8, 1925. fore provided an arrangement for selecting from the antenna any desiredl current vfrequency, 'and degree of it, for application to the input electrodes of three electrode vacuum is coupled to a second amplifier tube VT2 through a` non-selective impedance I shown in the ordinary symbol employed to indicate a so-called choke coil.

' There is shown coupled tothe plate circuit of tube VTl a variable period circuit L2C2 through a combined.electromagnetic and electrosatic coupling including inductive relation between coils-L1 and Lgrand condenser Cl common to the two circuits. yWith this arrangement, itis now possible, by reason of there'action that can be produced by this variable period circuit onto the plate circuit of tube VTl, to overcome the capacitive reaction of impedance I and the distributed i capacitiesof the plate circuit to'any desired degreefor any selected frequency, this being .because for any selected frequency there is anadjustment of thevariable period coupled circuit which will cause its reaction onto the plate circuit to beV inductive, which adjust- Y resonance. By adjusting the coupling to any desired amount, the degree of the inductive reactance can be controlled, and by adjusting the combined coupling to act with frequency in any predetermined way, .the variation of inlductive reactan'ce can be controlled with frequency in any predetermined way. The

manner in which these adjustments are obi; l tained ismore fully explained in copending applicationof S. Y. White, Serial No. 49,521, filed August yll, 1925, patented November 4, i930, No. 1,780,611. I

I 'Thus lwith the arrangement outlined, it is 9 possible to make the reaction ofthe plate circuit for any current frequency selectively applied to the input electrodes of tube VTl of any character and degree desiredso that the reaction through the inter-electrodal capacity can be made to lessen the degree of vdeamplification, to be neutral, or even to cause 'rcgenerative amplification. `Itis obvious that with increased amplification thus obtained the potential across impedance I is increased lWith'resulting increased effect on the second There isthere- `selective Yinput to tube VTl and 4 selective reactance controller for the output Tube VT3 is shown connectedA to act as av detector by reason of the grid condenser C4 shunted by the'grid leak resistance B, and having a grid return connected to the negative leg of the -filament circuit, the plate circuit including an audio .frequency transformer T, the primary beingby-passed by a condenser C5 as is usual practice. The detector `tube is coupled to the second amplifier tube throu `h an ad'ustable eriod circuit L2 C2 vand a combined electromagnetic and electrostatic coupling involving the inductive i'elations'between coils Ll and IN2, and the coupiling' condenser C2, thus making it possiblev to continue the control of transfer of energyY with frequency throughout th-e system. The vacuum tubes are indicated as energized in a conventional manner from sources of'energy supply marked l--A -B, A, '+B low, and +B high, the plates of the tubes being energized through choke coils K1 and Kg-of low distributed capacity toconfine high frequency j current flow to the desired circuits ofthe system. It will be noted that the'coupling condenser Cl serves the additional purpose of ypreventing the high potential appliedto the plate of tube VTl from reaching the grid of tube VT2. Y f

The second embodiment of our invention Vis shown in Fig. 3, which in general arrangement is the same as the system of Fig. 2, but

differs from `the arrangement of Fig. 2 in the connections employed foroverconiing the capacitive reaction'of the coupling impedance and distributed capacities. In the second eriibodiment the connection is made from the plate circuit of tube VT1 through acondenser C3 back Vto the antenna A,A the circuit of this connection being completed through coil L1, coupling condenser C1, and thence to the filament of the tube. This connection provides for the circuit L202 acting as the variable period c-ircuit to control the reaction of the plate circuit of tube VT1 with frequency, and therefore takes the place'of variable period circuit L2CL` in the embodiment of Fig. 2.

ByV this arrangement circuit -LZC2 is utilized l IGS to serve a double function, namely acting as acting as a circuit of the same tube.; VVhile'the coupling betweenkr the antenna and theY secondary may not be just of plate circuit reaction control, yet the reaction on the by proper selection of` values of condenser C3, so that all functions desiredmay readily be co-ordinated. In practice itisfound that with this second embodiment tube V'I1 can be caused to amplify through neutral to re` generative amplification with a degree of coupling between plate circuit can be controlled` the antenna andsecondary cirthat desired for the proper degree Y same natural periods,

cuit, that is entirely suitable for transfer of energy between these circuits. There therefore results a control of the potential developed across the-coupling impedance I, and therefore on the input 'electrodes of second vacuum tubes VT2. f

This second embodiment has the advantage that substantially the same result as that obtained in the first embodiment of Fig. 2 is s-ecured without the use of a second variable period circuit, and therefore greatly simplifies the construction and operation of the system. It will be noted that in the second embodiment, a condenser C6 is employed-toprevent the high potential applied to the plate of tube VT1 reaching the grid of tube V'Ig. It is desirable to make the capacity of this condenser sufhciently large to keep its reaction to currents of the Vfrequencies being handled loiv. In other respects, except for the method of control of the reaction of the plate circuit, the system is the same as that described in detail in connection with Fig. 2. A particular advantage of our system is a substantially complete isolation ofthe adjustable period circuits one from the other so far as influences which take place through the elements'and circuits of the system are concerned, and this is particularly true of the embodiment of Fig. 8. In the common practice of multiple stage selective amplification when the several stages are directly connected through adjustable period circuit great difficulty has been had in keeping any degree of independency of the several circuits and several stages of amplification. In such systems the variation of onepcircuit, though it might be intended to influence but one stage in the system, by reason of the close relations and reactions introduced through the enormous effects on the amplifying abilities of the tubes, upsets the system as a Whole, With the result that the greatest difficulty has been encountered in attempting to build multiple stage amplifying units having a fair degree of efficiency, and the problem has been rendered doubly difcult in trying to simultaneously operate all the controls from a common control element. In our system these difficulties are enormously reducedby reason of the substantially total independency of the several adjustable period circuits,`and it is possible to employ as many'units of this system in cascade as may be desired for any degree of amplification at one and the same frequency, as coi'npared to the practical limits heretofore reached in the directly connected systems. f

In Ythe systems of both Figs. -2 and 3, it is preferable to employ choke coils K2 of substantially different natural period from choke coils K1, as if the tvvo coils are of nearly the it is possible for-KL to react on K1L through the internall capacity of tube V'Iz 'to create an oscillating system at V the tube output of said some arbitrary frequency, which would result in a parasitic undesirable effect.

While We have illustrated and described our invention in connection with radio receivers, Avve dov not intend any limitations therein, as many applications are obvious to those skilled in the art.

We claim 1. Themethod of selectively amplifying alternating currentsvvhich comprises selectively impressing said currents upon a three electrode vacuum tube, non-selectively transferring the tube output of said currents to a second tube, and selectively controlling the amplifying ability of said first tube independently of said step of selectively impressing said currents upon a three electrode tube.

leo

2. The method of selectively amplifying v alternating currents Which comprises selectively impressing said currents upon a three electrode vacuum tube, non-selectively developing and impressing on a second vacuum tube capacitively reacting potentials from currents, and selectively producing an inductive reactance in the output circuit of said first tube.

3. The method of selectively but uniformly amplifying alternating currents over a range of frequencies Which comprises selectively impressing said currents upon a three electrode vacuum tube, non-selectively transferring the tube output of said vcurrents to a second tube, and selectively butuniformly -controlling the amplifying ability of said first `tube With frequency independentlyV of said step ofselectively impressing said currents u on a three electrode tube.

4. The method of selectively but uniformly amplifying alternating currents over a range of frequencies which comprises selectively impressing said currents upon a three electrode vacuum tube, non-selectively developing and impressing on asecond'vacuumtube capacitively reacting potentials from the tubeV output of said currents, and selectively producing in the output circuit of said rst tube an inductive reactance quency in like manner to the reactance variation of said capactively reactingimpedance Wit-h frequency. v Y 5. The method of selectively highlyV amplifying alternating currents of amaintained one-frequency Without deleterious reaction of succeeding selective circuits on preceding selective circuits Whichcomprises selectively impressing said currents upon a three electrode vacuum tube, non-.selectively transferring the tube output of said currents' to a second tube, selectively controlling the amplifying ability of said first tube independently of said step of selectively impressing said currents upon a three electrode tube, selectively transferring said currents from said second tube to a succeeding like system and repeating the operation until the desired deico that varies with fre- Y 25 coupling.

grec,y of vone-frequency amplification is obfirst Atube from rvthat coupling', and

tained. n

' 6. A system foi' the selective amplification ofl alternating currents including a three electrode vacuum tube having' variable means for selectively impressimgl said currents thereon, a second tube, non-selective'l impedance means coupling the input of said second tube to the output of said first tube, and variable means lother than said first mentioned variabley means for selectively controlling the amplifying' ability of said first tube.v with frequency. v Y

'7. A system for the selective amplification of alternatinggr currents including' a three electrode vacuum tube having' variable means for selectively impressing' said currents thereon, a second tube, non-selective impedance means coupling the input of said second tube to the output of said firsU otherl than said first mentioned variable means for selectively changing' With frequency the output circuit reactance of said firsttu'be from that due to said impedance `8. A system for the selective amplification of alternating' Vcurrents includingua three electrode vacuum tube having variable means for selectively impressing said currents thereon, a second tube, `non-selective impedance means coupling' the input of said-second tube to the output of said 'first tube, variable mea-ns other than said first mentioned variable means for selectively changing with frequency the output circuit reactance of said means for maintaining the changed reactanee constant 9. A system for the selective of alternating' currentsincluding` Vamplifieation a three electrode vacunmtubeliaving variable means for electrode selectively impressing said currents thereon,

a second tube, non-selective capacitively reacting impedance means linking' the input of said second tube to the output of said first tube, and variable means oth i' than said first mentioned variable means for selectivelyv impressing with frequency lan inductive reac-V tion on said output circuit Yof saidrfirst tube.

10. A system for thev selective amplification of alternating' currents includinga three electrode -vacuum tube having'rmeans for selectively impressing' said currents thereon, a: second tube, a non-selective capacitively i'eacting impedance linking the inputof said second-tube to the output of said first tube, means for'selectively impressing' with frequency an inductive reaction on said output circuit of said first tube, and means forinaintaining' Vthe relation of said inductive reactionto the capacitive reaction of .ance consant with frequency.

11. A'system foi` the selective amplification of alternating currentsincludingr a three vacuum tube having variable tube, land variable meansV due to said impedanceV [with frequency..

said impedi lperiod circuit coupled to the output circuit of said first tube, and Vmeans fo-r controlling the coupling between Vsaid variable circuit and said output circuit with frequency.

13. A systemfor the selective amplification of alternating currents including' a three electrode vacuum tube, a variable period Vcircuit connected to the input electrodes ofsaid tube,

a second tube, anon-selective impedance linking the input of said second tube to the .output ofv said first tube, and a coupling .between the output circuit ofY said firsttube and said variable` period circuit^` 14. A system for the selective` amplification of alternatingcurrents includingr a three electi'ode vacuum tube, a variable period circuit connected to the input electrodes of said tube, a second tube, a non-selective `impedance linking the input of saidsecond tube to the output of said first tube, a coupling between the outputcircuit of said first tube and said --variable period circuit,rand means for controlling said coupling' Withfr'equency.

electrode vacuum tube, a variable period ci-rcuit connected tothe input electrodes of said tube, a second tube,a non-selective impedance linking .the input of said second tube to the output of said first tube, a couplingvbetween the output'circuit of said first tube and said` and a condenser in series With tube, and anon-selective impedance in the output of the second'tube of different natural4 period thanV said first impedance;

17. The method ofselectively amplifying alternatingr currents which comprises selectively impressing, said currents upon armultielectrode electrony discharge tube, *non-selec?,

system for; the-selective amplification of alternating'currentsincludinga three tube, anon-selective impedl tively transferring the tube output of said currents to a second tube, and selectively but independently controlling the amplifying ability of said tube in consonance with the selective impressing of currents thereon.

18. A system for the selective amplification of alternating currents including a multi-electrode electron discharge tube having` a variable period circuit connected across the input electrodes thereof, a second tube, means for non-selectively transferring from the output of said rst tube to the input electrodes of said second tube the first tube output of said currents, and means for selectively but independently controlling the amplifying ability of said first tube in consonance with selected tuning of said variable circuit.

EDWARD I-I. LOFTIN. SIDNEY Y. WHITE. 

